Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$45.92	7.802%	$49.5027	$49.50	$49.50	$49.50
Purchase #2	$16.98	11.528%	$18.9375	$18.94	$18.95	$18.90
Purchase #3	$34.33	9.418%	$37.5632	$37.56	$37.55	$37.60
Purchase #4	$158.60	11.580%	$176.9659	$176.97	$176.95	$177.00
Purchase #5	$171.31	13.312%	$194.1148	$194.11	$194.10	$194.10
Purchase #6	$156.92	13.696%	$178.4118	$178.41	$178.40	$178.40
Purchase #7	$247.90	3.196%	$255.8229	$255.82	$255.80	$255.80
7 purchase totals =	$831.96		$911.3188	$911.31	$911.25	$911.30